Abstract
The rise in multidrug resistant bacteria is an area of growing concern and it is essential to identify new biocidal agents. Cationic grafted compounds were investigated for their antimicrobial properties using minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) tests. Synergy testing was carried out using the compounds in the presence of ultraviolet (UV). Fractional inhibitory concentration (FIC) and fractional bactericidal concentration (FBC) tests were carried out using the cationic molecules in conjunction with metal ion solutions of gold, silver, palladium, platinum, rhodium, titanium, tin, vanadium and molybdenum. Individually, the cationic compounds containing quaternary amines, polyphenylene vinylene (PPV) with long polyacrylate grafts (PPV-g-PMETAC (HMw)), polyphenylene ethylene (PPE) with long polyacrylate grafts (PPE-g-PMETAC (HMw)), polyphenylene vinylene (PPV) with short polyacrylate grafts (PPV-g-PMETAC (LMw)) and polyphenylene ethylene (PPE) with short polyacrylate grafts (PPE-g-PMETAC (LMw)) were effective against Enterococcus faecium. The most successful compound under UV was PPV-g-PMETAC (HMw). Following the FICs, palladium and rhodium ion solutions caused a synergistic reaction with all four tested compounds. The presence of conjugated bonds in the cationic molecules increased its antimicrobial activity. These results suggest that the chemical backbone of the compounds, alongside the chain lengths and chain attachment affect the antimicrobial efficacy of a compound. These factors should be taken into consideration when formulating new biocidal combinations.
Highlights
Antimicrobial resistance (AMR) is a serious worldwide issue, with our ability to treat many infections becoming increasingly difficult
When the compounds were tested against E. faecium, it was demonstrated that all the gra ed poly(para-phenylene ethynylene) (PPE) or poly(para-phenylene vinylene) (PPV) compounds demonstrated greater antimicrobial activity compared to the ungra ed polyphenylene ethylene (PPE) (1250 mg mLÀ1) or polyphenylene vinylene (PPV) (1250 mg mLÀ1) alone (Table 2)
A er 30 min of UV exposure all the compounds demonstrated an increase in antimicrobial efficacy, with PPV-g-PMETAC (HMw) once again being the most active (39.1 mg mLÀ1)
Summary
Antimicrobial resistance (AMR) is a serious worldwide issue, with our ability to treat many infections becoming increasingly difficult. Cationic antimicrobials have been widely deployed in antisepsis for well over half a century without any apparent reduction in their effectiveness.[1] Cationic compounds have an overall positive charge, which in uences the interactions between the molecule and the bacterial cells.[2] Conjugated polyelectrolytes (CPEs) have attracted much attention in recent years as a new class of materials.[3,4,5] Within the diverse categories of synthesised CPEs, modi ed-charge CPEs have been shown to demonstrate antibacterial efficiency, which has been attributed to their structure.[6,7,8,9]. The antimicrobial ability of compounds can be altered or improved by the manipulation of speci c variables or by using them in combination with other treatments to yield synergistic
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